1. Field of the Invention
The present invention relates to a head suspension for a hard disk drive incorporated in an image processing unit such as a computer.
2. Description of Related Art
FIG. 1 shows part of a hard disk drive. The hard disk drive includes disks 2 serving as storage media. Data is written to and read from the disk 2 with a magnetic head 11 that is supported with a head suspension 101. The head suspension 101 is attached to an arm 31. The arm 31 is attached to a carriage 13, which is turned around a spindle (not shown) by a positioning motor (not shown). The head suspension 101 includes a base plate 32, a load beam 102 extending from the base plate 32 to the head 11, and a flexure 103.
The load beam 102 is made of, for example, a stainless steel (Japanese Industrial Standard: SUS304, SUS301, or the like) plate having a thickness in the range of 30 μm to 60 μm. The flexure 103 includes a substrate made of a stainless steel (SUS304) plate or a spring plate having a thickness of about 20 μm, an insulating layer formed on the substrate from, for example, polyimide resin, and a conductive layer made of, for example, copper by deposition or photolithography on the insulating layer. On the conductive layer, a protective layer is usually made from insulating material such as polyimide or epoxy resin. The total thickness of the flexure 103 is about 40 μm.
The arm 31 and base plate 32 are usually discrete parts. There is an integrated arm (called “unamount arm”) that is an integration of an arm and a base plate. The arm and base plate are collectively called “base” (12) hereinafter. The base plate 32 has a thickness of 200 μm to 300 μm. The bending elastic modulus of the base plate 32 is larger than that of the load beam 102 by one digit.
The load beam 102 includes a rigid part 21, a resilient part 22, and a joint part 105. The resilient part 22 is bent by a predetermined amount toward the disk 2, to apply a gram load onto the head 11 so that the head is pressed against the disk 2. The joint part 105 of the load beam 102 is laid on and fixed to a surface of the base 12. The flexure 103 transmits data to and from the head 11. Between the head 11 and the joint part 105 of the load beam 102, the flexure 103 is laser-welded at several spots to a surface of the load beam 102 that faces the disk 2.
The head 11 lifts from the surface of the disk 2 due to an air flow when the disk 2 is rotated. It is preferable that a force to lift the head 11 balances with the gram load of the head suspension 101 so that the head 11 is stably kept at a slightly lifted position. For this, adjusting the gram load by bending the load beam 102 is essential to determine the performance of the hard disk drive. If the gram load is determined solely with the bending stress of the resilient part 22 of the load beam 102, the designing of the head suspension 101 will be easy.
In practice, however, the bending stress of a combination of the resilient part 22 of the load beam 102 and the flexure 103 arranged in parallel with the resilient part 22 works on the head suspension 101. FIG. 2 is a perspective view showing an example of a head suspension 101 according to a related art. Like the head suspension 101 of FIG. 1, the head suspension 101 of FIG. 2 includes a load beam 102, a flexure 103, and a base plate 32 serving as a base 12. The load beam 102 includes a rigid part 21, a resilient part 22, and a joint part 105. FIG. 3 is an enlarged sectional view showing the resilient part 22 indicated with arrows III in FIG. 2. In FIGS. 2 and 3, the flexure 103 and rigid part 21 are fixed together at a joint spot X, the flexure 103 and a flexure attaching face 107 of the joint part 105 are fixed together at a joint spot Y, and the joint part 105 and base 12 are fixed together at a joint spot Z. The joint spot Y is separated away from the joint spot Z toward a disk, and therefore, the flexure 103 restricts movement of the resilient part 22. Namely, a gram load acting on a head 11 is not determinable only with the bending stress of the resilient part 22 but it is greatly influenced by the bending stress of the flexure 103.
In addition, due to temperature and humidity, the flexure 103 extends or contracts, and the elastic modulus thereof varies. If a proportion of the flexure 103 in the gram load is large, the gram load easily varies to raise a severe problem in designing the head suspension 101.
The related art mentioned above is disclosed in Japanese Unexamined Patent Application Publication No. 11-514780.